Field of the Invention
The present invention relates to a process for building tyres and to a tyre obtainable by said process.
Description of the Related Art
A tyre for vehicle wheels generally comprises a carcass structure including at least one carcass ply having respectively opposite end flaps in engagement with respective annular anchoring structures, integrated into the regions usually identified with the name of “beads”, defining the radially internal circumferential edges of the tyre.
Associated with the carcass structure is a belt structure comprising one or more belt layers, placed in radially superposed relationship relative to each other and to the carcass ply and having textile or metallic reinforcing cords with a crossed orientation and/or substantially parallel to the circumferential extension direction of the tyre. At a radially external position to the belt structure a tread band is applied that is also made of elastomeric material like other semifinished products constituting the tyre.
In addition, respective sidewalls of elastomeric material are applied at an axially external position, to the side surfaces of the carcass structure, each extending from one of the side edges of the tread band until close to the respective annular anchoring structure to the beads.
In tyres of the tubeless type, an airtight coating layer usually termed “liner” covers the inner tyre surfaces.
Within the present specification and the appended claims, by the term “elastomeric material” it is intended a compound comprising at least one elastomeric polymer and at least one reinforcing filler. Preferably, this compound further comprises additives such as cross-linking agents and/or plasticizers. Due to the presence of the cross-linking agents, this material can be cross-linked by heating so as to form the final article of manufacture.
In tyres intended for particularly heavy-duty vehicles and/or for High Performance and Ultra High Performance cars and racing cars, application of so-called “cushion inserts” is required which are disposed astride the side, i.e. axially external, edges of the belt layers to protect the carcass plies and/or other adjacent components from direct contact with the ends of the metal cords forming the belt structure.
In traditional processes for tyre manufacture, the carcass structure and belt structure, together with the respective tread band, are provided to be made separately from each other through assembly of semifinished components at respective work stations, to be mutually assembled at a later time, as disclosed in document U.S. Pat. No. 3,990,931 or document EP 0 613 757, for example.
In relatively recent times, production processes have been developed which are such conceived as to avoid production and storage of semifinished products. For instance, in document WO 01/36185 in the name of the same Applicant, a robotized arm carries a toroidal support on which each of the components of a tyre under production is directly made. The robotized arm gives the toroidal support a circumferential distribution motion around its geometric axis, simultaneously with controlled transverse-distribution displacements in front of a member supplying a continuous elongated element of elastomeric material. The continuous elongated element thus forms a plurality of coils the orientation and mutual-superposition parameters of which are managed in such a manner as to control variations in the thickness to be given to a component of a tyre being manufactured, based on a predetermined laying scheme previously inputted into an electronic computer.
EP 0 976 585 discloses a cushion insert formed with an outer layer and an inner layer of different compositions, in which the outer layer has a 100% higher module than that of the inner layer, and the inner layer has a 100% higher module than that of a rubberizing material of the belt layer onto which the cushion insert is applied.
EP 1 170 151 discloses a cushion insert separating the end portions of two adjacent belt layers. The cushion insert extends in an axially external direction from one end of one of the belt layers of smaller width, and comprises an inner portion separating the end portions of the belt layers from each other, and an outer portion extending from the inner portion to the outside of the tyre and having at least two different elastomeric compositions, the elasticity moduli of the different portions of which have a predetermined mutual relation.